1. Field of the Invention
The present invention relates to a mechanical breathing aid of the type having an adaptive expiration control.
2. Description of the Prior Art
A breathing aid is known from U.S. Pat. No. 4,448,192 that adapts to a patient's efforts at breathing and to the patient's change in respiratory requirements. An adaptive pressure/volume (P-V) control law is employed for regulating the operation of the breathing aid during one or both of the inspiration phase and the expiration phase of the breathing cycle of the patient. The control law is repeatedly modified for a particular phase dependent on gas parameters measured during the same phase of previous cycles with the goal of enabling the patient to breath with a minimum ventilation opposition, or fighting.
In this known breathing aid the modification of the control law is carried out using estimations of lung compliance and resistance made iteratively over a number of breathing cycles and using fixed adaptation rules. However, the more active the patient the less applicable these rules become, to the extent that in this known breathing aid any measurements made during significant patient activity are ignored in the modification of the control law. Thus a relatively large number of breathing cycles may be required before an optimum adaptation is provided.